Field of the Invention
The invention relates to a method and a control device for the operation of a transmission system for an IO link according to the independent claims.
State of the Art
In the field of machinery and plant engineering as well as in automation engineering numerous standardized field bus systems have proven to provide good alternatives to parallel individual wiring. Here, a plurality of so-called field bus modules is connected to a central control device via the field bus. In turn, terminal devices are connected to the field bus modules.
More recently, so-called “IO link” connections have been used for connecting the terminal devices to the field bus modules. Such an IO link as well as a method and a control device for the operation of such an IO link follow from DE 10 2012 009 494 A1. As is described therein, the field bus modules take over the role of an IO link master. As terminal devices (referred to as “IO link devices” in the following) sensors, actuators, display devices, operator devices, or smaller drives in machines may be used, for example.
In many assembly facilities the space requirements for the cable system and the switch box for the electrical installation often exceed the available installation space of the mechanical handling system. Almost always the costs for the work hours as well as for the material required for the installation of the hardware for signal transmission to the machine exceed the purchasing costs of the connected binary sensors and actuators.
In order to tackle this problem, a consortium of involved manufacturers has specified a standard for an intelligent sensor/actuator interface for which the mentioned term “IO link” is used, wherein it is planned to standardize it as an international open standard in the norm IEC 61131-9. According to this said IO link devices are described through description files IODD, IO link device description. In addition, IODD is to be standardized as a description language as an open standard in the norm ISO 15745.
Such an IO link provides a serial point-to-point connection for signal transmission between sensors and actuators and the TO level of the machine. In principle, an IO link transmits data between a said IO link master and a connected IO link device as the slave. As IO link masters, field bus modules as well as SPS (Sensor Planning Service) interface assembly groups are available.
In addition, such an IO link is downward compatible to binary standard sensors and generally uses unshielded three- or five-wire standard cables. While the field bus level is responsible for interconnecting individual machines or their components with the control system of the plant, the IO link is assigned to the machine or sensor-actuator level. The field bus level comprises most of the standardized field busses such as are generally used in machinery and plant engineering.
Commonly used field busses are, for example, PROFIBUS-DP, Interbus, DeviceNet, CC-Link and CANopen. More recently, also Ethernet-based field bus standards such as PROFINET, EtherNet/IP, EtherCAT as well as Ethernet POWERLINK have been used. Field busses are used in a particularly advantageous manner for bridging greater distances between individual participants, which can lie between several 100 meters up to sometimes more than 10 km. However, it is problematic and disadvantageous that it is practically impossible to use these high-performance bus systems on the sensor-actuator level in an economically viable manner.